ANONYMOUS wrote: Technically this depends on what the questions ask for, but you will notice that all the questions in the sample exam ask for a "justification". This is not asking for a formal proof, just an argument to convince the reader that your algorithm is correct (for all inputs). As I have said previously in this unit, the rule of thumb I suggest you use when writing such an argument is that it should be sufficient to convince a fellow student in the unit that your algorithm is correct. Therefore imagine being on the other side of this. Read your argument and see if there is anywhere you could poke holes in it or where it makes a logical leap that seems unfounded. Even better, practise with other students writing arguments to convince each other and trying to pull them apart. Hope that helps. Gozz